A Primer on COL4A1/COL4A2-Related Cerebral Small Vessel Disease for Neurologists

COL4A1 and COL4A2 encode type IV collagen, a principal structural component of basement membranes, and pathogenic variants in these genes cause a multisystem small vessel vasculopathy with prominent cerebrovascular involvement. Despite increasing recognition with the expansion of genetic testing, COL4A1/2-related cerebral small vessel disease remains underrecognized in clinical practice, in part due to its striking phenotypic heterogeneity. Presentations span a broad clinical spectrum-from asymptomatic individuals or incidental imaging findings to recurrent ischemic events, intracerebral hemorrhage, and catastrophic perinatal brain injury-and may occur across the lifespan. In this narrative review, we provide a clinically oriented framework for recognizing and managing COL4A1/2-related cerebral small vessel disease. We integrate underlying molecular mechanisms of type IV collagen dysfunction with vascular pathophysiology, highlighting how impaired basement membrane integrity leads to a dual hemorrhagic-ischemic phenotype. We describe characteristic neuroimaging patterns, including microhemorrhages, white matter hyperintensities, lacunes, and dilated perivascular spaces, and emphasize their anatomic distribution and clinical relevance. Given the systemic nature of the disorder, we also review key extracerebral manifestations-including ocular, renal, and musculoskeletal features-that serve as important diagnostic "red flags." We outline practical considerations for clinical care, including indications for genetic testing, initial diagnostic evaluation, and longitudinal management strategies tailored to neurologists. Particular emphasis is placed on individualized decision-making around antithrombotic therapy, hemorrhage risk mitigation, and surveillance for complications such as intracranial aneurysms. Illustrative multigenerational cases are incorporated to demonstrate genotype-phenotype correlation, incomplete penetrance, and common diagnostic pitfalls. By providing a mechanism-informed and clinically actionable synthesis, this review aims to improve recognition, reduce misdiagnosis, and guide management of COL4A1/2-related cerebral small vessel disease.